Can valve cover gasket leak cause boost/vacuum leak?

Tengoku · 09-25-2011, 09:12 PM

My valve cover gasket has been leaking a little bit of oil from the bottom. My question is, can a blown seal cause boost/vacuum leak? Because I know that PVC hose is connected to the top of it. I've been noticing loss of power and throttle response.

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Tengoku · 09-26-2011, 10:23 AM

Does anyone have any idea?

Steve.804 · 09-27-2011, 12:13 PM

Yes a bad enough gasket leak can cause a vacuum leak, but I would think you'd get a CEL to come on if it's making any substantial difference.

2Fast4U1DAY · 09-27-2011, 02:15 PM

Quote:

Originally Posted by Steve.804

Yes a bad enough gasket leak can cause a vacuum leak, but I would think you'd get a CEL to come on if it's making any substantial difference.

Think about what you just said. A valve cover leak is not a vacuum leak. There is no passage way into the combustion chamber through the cylinder head.

Op the pcv does not draw vaccum either. Pcv sends crankcase pressure out through the hose, and back into the intake post MAF sensor (regulated by the spring inside the valve itself).

bluescoobywagon · 09-28-2011, 11:24 AM

If the engine is old enough to leak at the valve cover gaskets, it's also old enough to have vacuum leaks after the MAF. I would start there.

subi-T · 05-21-2015, 12:56 AM

Do you know what will happen if the hose on the right comes loose or of it comes off will it cause a lose of power and what is it called and what it is used for?
Thanks

b1gbleu · 05-22-2015, 12:06 PM

Those are breather hoses. Anything loose on three motors will cause idling/power issues.
Check all the smaller ones, they usually are not secured well and either fall off or split due to age.

DonnaMechanic_20 · 09-19-2020, 01:06 AM

[quote=Tengoku;35205662]My valve cover gasket has been leaking a little bit of oil from the bottom. My question is, can a blown seal cause boost/vacuum leak? Because I know that PVC hose is connected to the top of it. I've been noticing loss of power and throttle response.”

So this is difficult for a lot of people to understand I see. Someone commented about the PCV being after the pistons therefore not being able to cause vacuum from that perspective. But think of the PCV as apart of a cycle. ( ~> <~)It takes air that seeped past the piston and returns it to the intake manifold to be reburned so the air doesn’t cause too much pressure. If the valve cover is leaking and oil can get outside then air can definitely get inside because the Pcv is a vacuum! So in simple yes the valve cover can cause a vacuum leak. Many mechanics notice this leak and replace gaskets which solves the problem. But sometimes the oil leak isn’t the issue but the vacuum...

09-25-2011, 09:12 PM	#1
Tengoku Scooby Newbie Member#: 293241 Join Date: Sep 2011	Can valve cover gasket leak cause boost/vacuum leak? My valve cover gasket has been leaking a little bit of oil from the bottom. My question is, can a blown seal cause boost/vacuum leak? Because I know that PVC hose is connected to the top of it. I've been noticing loss of power and throttle response. * Registered users of the site do not see these ads.

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09-26-2011, 10:23 AM	#2
Tengoku Scooby Newbie Member#: 293241 Join Date: Sep 2011	Does anyone have any idea?

09-27-2011, 12:13 PM	#3
Steve.804 Scooby Specialist Member#: 68647 Join Date: Aug 2004 Chapter/Region: MAIC Location: Richmond, VA Vehicle: 07 STI 35R 05 BMW M3 ZCP	Yes a bad enough gasket leak can cause a vacuum leak, but I would think you'd get a CEL to come on if it's making any substantial difference.

09-28-2011, 11:24 AM	#5
bluescoobywagon Scooby Specialist Member#: 14911 Join Date: Feb 2002 Chapter/Region: MWSOC Location: The land of E85 Vehicle: Not A Wagon! 2011 WRX - 285s on 18x9.5	If the engine is old enough to leak at the valve cover gaskets, it's also old enough to have vacuum leaks after the MAF. I would start there.

05-21-2015, 12:56 AM	#6
subi-T Scooby Newbie Member#: 348082 Join Date: Feb 2013 Chapter/Region: SCIC Location: Downey CA Vehicle: 2006 impreza SGM	Do you know what will happen if the hose on the right comes loose or of it comes off will it cause a lose of power and what is it called and what it is used for? Thanks

05-22-2015, 12:06 PM	#7
b1gbleu Scooby Newbie Member#: 402402 Join Date: Sep 2014	Those are breather hoses. Anything loose on three motors will cause idling/power issues. Check all the smaller ones, they usually are not secured well and either fall off or split due to age.

09-19-2020, 01:06 AM	#8
DonnaMechanic_20 Scooby Newbie Member#: 518695 Join Date: Sep 2020	[quote=Tengoku;35205662]My valve cover gasket has been leaking a little bit of oil from the bottom. My question is, can a blown seal cause boost/vacuum leak? Because I know that PVC hose is connected to the top of it. I've been noticing loss of power and throttle response.” So this is difficult for a lot of people to understand I see. Someone commented about the PCV being after the pistons therefore not being able to cause vacuum from that perspective. But think of the PCV as apart of a cycle. ( ~> <~)It takes air that seeped past the piston and returns it to the intake manifold to be reburned so the air doesn’t cause too much pressure. If the valve cover is leaking and oil can get outside then air can definitely get inside because the Pcv is a vacuum! So in simple yes the valve cover can cause a vacuum leak. Many mechanics notice this leak and replace gaskets which solves the problem. But sometimes the oil leak isn’t the issue but the vacuum...